particles that are 14 microns and larger. It is necessary to use a
3-micron filter with a beta rating of 75 or higher to achieve this
level. The oil should be sampled regularly to ensure the system
meets this standard. A higher ISO code may mean the filters
aren't being changed often enough, the filters don't have the
proper micron and beta rating, or additional filters may need to
be added to the system.
In conclusion, by troubleshooting systems that utilize propor-
tional valves, you can avoid lost production time as well as the
unnecessary expense of sending off good valves for repair.
Changing out parts that do not need to be replaced can also
introduce contaminants into the system, which can lead to even
more serious problems. Be sure to follow the steps described in
this article before removing any proportional valves from your
hydraulic systems.
About the Author
Al Smiley is the president of GPM Hydraulic Consulting Inc., located
in Monroe, Georgia. Since 1994, GPM has provided hydraulic training,
consulting and reliability assessments to companies in the United
States, Canada, the United Kingdom and South America. Contact Al at
gpm@gpmhydraulic.com.
Figure 8. A proportional valve tester
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